wrapper classes in java

1Wrapper classes: classes that are dedicated to primitives        
2Byte, Short, Integer, Long, Float, Double, Character, Boolean
3presented in "java.lang" package
4AutoBoxing: converting primitive values to wrapper class
5		int a = 100;
6		Integer b = a  // auto boxing
7Unboxing: converting wrapper class value to primitives
8		Integer a = 100;
9		int b = a;  // unboxing
10	int a = 100;
11	double b = a;    // none
12

1public class CommandLineArguments {
2    public static void main(String[] args) {
3        int a = Integer.parseInt(args[0]);
4        int b = Integer.parseInt(args[1]);
5        int sum = a + b;
6        System.out.println("Sum is " + sum);
7    }
8}
9

1
2public class HelloWorld {
3  public static void main(String[] args) {
4    
5    // how to use class in java
6    class User{
7    	
8    	int score;
9    }
10    
11    User dave = new User();
12    
13    dave.score = 20;
14    
15    System.out.println(dave.score);
16    
17 
18  }
19}
20

1In Java, for each Primitive type, there is a matching class type.
2  We call them Wrapper classes:
3	Primitive types are the most basic data types
4    available within the Java language. 
5	There are 8: boolean , byte , char , short ,
6                  int , long , float and double . 
7	These types serve as the building blocks of
8    data manipulation in Java.
9	Wrapper classes: Byte, Short, Integer, Long,
10                 Float, Double, Boolean, Character
11			
12	All the wrapper classes are subclasses
13    of the abstract class Number. 
14	The object of the wrapper class contains or
15      wraps its respective primitive data type. 
16	Converting primitive data types into object
17    is called boxing, and this is taken care by the compiler.
18			
19			Differences: 
20				1. Wrappers classes are object 
21				2. null can only be assigned to classes
22				3. Wrapper class does have methods
23				4. Primitives does have default values
24						default value of primitives:  
25								 byte, short, int, long ==> 0
26								 float, double ==> 0.0;
27								 boolean ==> false;
28								 char ==> space		 
29				5. Default values of wrapper class: null
30

1ArrayList<Integer> myNumbers = new ArrayList<Integer>(); // Valid
2

1ArrayList<int> myNumbers = new ArrayList<int>(); // Invalid
2